In the related art, there is known a vehicle seat slide device which is described in EPU: 2886389A1 (Reference 1), for example. The vehicle seat slide device is configured to include a lower rail which extends in a front-rear direction of the vehicle, an upper rail which is joined to the lower rail to be capable of moving relative thereto, and a locking member (a lock member) capable of restricting the movement of the upper rail.
In other words, as illustrated in FIG. 7, a lower rail 110 includes a pair of side wall portions 111 provided to line up in a width direction, a base wall portion 112 which connects the base ends (the bottom ends) of the side wall portions 111 in the width direction, a pair of inward-extending wall portions 113 which overhang from the tips (top ends) of the side wall portions 111 to the inside in the width direction in which the inward-extending wall portions 113 approach each other, and a pair of downward-extending wall portions 114 which overhang downward from the tips of the inward-extending wall portions 113.
An upper rail 120 includes a main body portion 121 which stands vertically between the downward-extending wall portions 114, and a pair of flanges 122 which overhang from the tip (the bottom end) of the main body portion 121 to the outsides in the width direction and are further folded so as to be surrounded by the side wall portions 111, the inward-extending wall portions 113, and the downward-extending wall portions 114.
Both the lower rail 110 and the upper rail 120 have symmetrical (laterally symmetrical) rail cross sections in the width direction thereof, and are mainly prevented from dislocating in an up-down direction by the engagement of the inward-extending wall portions 113, the downward-extending wall portions 114, and the flanges 122. It goes without saying that the engagement state of the lower rail 110 and the upper rail 120 is substantially fixed along the entire length in a longitudinal direction thereof.
As illustrated in FIGS. 8A and 8B, a reinforcement member 130 is bonded to the rear end of the lower rail 110. The reinforcement member 130 is formed of reinforcement plates 131, which are formed of a pair of plate materials provided to line up in the width direction, and each of the reinforcement plates 131 includes an inward-extending wall reinforcement portion 133 and a side wall reinforcement portion 132, and is substantially L-shaped. The side wall reinforcement portions 132 cover the side wall portions 111, and the inward-extending wall reinforcement portions 133 cover the inward-extending wall portions 113.
Here, for example, when the lower rail 110 receives input of a significant load upward from the seat side (for example, a seatbelt) which is supported by the upper rail 120 due to a frontal collision of the vehicle, the lower rail 110, the inward-extending wall portions 113 or the like of which are pressed by the flanges 122 of the upper rail 120 which is pulled upward, deforms (so-called separating deformation) such that the opening end side thereof opens. Favorable energy absorption with the deformation is realized due to the deformation of the lower rail 110 at this time transitioning in a similar manner to that presumed during design.
In particular, due to the reinforcement member 130 being bonded to the rear end of the lower rail 110, it is considered possible to delay the separating deformation of the lower rail 110 when a large load is input. This is because, ordinarily, during a frontal collision of the vehicle, since the deformation of the lower rail 110 generally proceeds from the rear toward the front, the rear-to-front deformation is suppressed at the starting time of the deformation.
Due to the reinforcement member 130 evenly covering the side wall portions 111 and the inward-extending wall portions 113 using the side wall reinforcement portions 132 and the inward-extending wall reinforcement portions 133, the separating deformation of the lower rail 110 when a large load is input may be impeded, and the lower rail 110 may break. The deformation mode of the lower rail 110 caused by the breaking lacks regularity in the affected parts, the occurrence timing, and the like, and is unstable in comparison to the separating deformation mode.